Batman/Spiderman/Superman etc. all have theirs. This thread is to speculate on how the writers and Jon will make their hero understandable to the audience. We know Tony first had the armor to save his life, but after that why did he decide to be a superhero? I think this is a crucial point that the filmmakers need to get right in order to have a real success.

I think it came down to two things, one, he wanted to use his technology to make the world safer and help the common citizen and second was to atone for his mistakes, one of which was the weapons he and his father made that killed so many innocent people, you see this as a reader in Armor Wars, he has his technology stolen and all he see's is what would happen to innocent people if the tech fell into criminal hands, he himself goes on a one man crusade to stop every armored villian and hero to make sure this doesn't happen.
Those are my views as why he becomes a hero.

I think it came down to two things, one, he wanted to use his technology to make the world safer and help the common citizen and second was to atone for his mistakes, one of which was the weapons he and his father made that killed so many innocent people, you see this as a reader in Armor Wars, he has his technology stolen and all he see's is what would happen to innocent people if the tech fell into criminal hands, he himself goes on a one man crusade to stop every armored villian and hero to make sure this doesn't happen.
Those are my views as why he becomes a hero.

The cartoon DuckTales basically took and parodied the entire thing with Gizmoduck. He was Scrooge's bodyguard and personal protector, but he also stopped villains whenever they reared their heads in Duckburg. Basically he moved up to being a full fledged hero after just being a bodyguard.

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If the person you're seeing ever asks the question "Who is Stan Lee?", promptly kick their ass to the curb.
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Who the **** makes a movie and while planning it is like, "you know what this needs...is some Greg Kinnear."

I thought it was beause his Father beleived he was a lousy, good for nothing playboy, so he decided to use his technology for good.

Partially, Tony's father was disappointed with the path Tony was taking, Tony wanted to live the life of fun and pleasure, Howard wanted Tony to follow in his footsteps, Howard knew Tony was brilliant but felt he was wasting his talents on booze and women, it was only after Howard and Maria's death did Tony realize his mistakes and dedicated himself to making Stark International a powerful corporation which included weapons manufacturing.
Iron Man came about from Tony's injury and he realized he could do even more good on a global scale as a superhero.

Part of what makes the character interesting to me is that his motivation isn't always entirely atruistic --- at least a part of it is about pure ego. Showing off to the world, saving the girls.... unlike many other superheroes, Tony Stark is the same guy in and out of the armor. This ego's also shown even by small details like the way he keeps having to make his armor better and better instead of ever settling.

But at the same time.... what it really comes down to, the real motivation, is redemption. Being a hero like Iron Man is Stark's way of redeeming himself for all his many past sins.